Discarded tires represent a considerable material flow of a relatively homogeneous type of scrap. Approximately 511,000 t of tires accumulate annually in Germany as discarded tires from the replacement business in the area of repair shop waste disposal and in replacement part retail, approximately 9,000 t of discarded tires are imported, and approximately 65,000 t of discarded tires come from the recycling of discarded vehicles. Thus annually around 585,000 t of tires await further use, recycling or removal in Germany.
Today, a major part of the discarded tires is recycled as energy. Thus, for years, the cement industry has already been using discarded tires as a fuel value-rich secondary raw material for its kilns. Approximately 72,000 t of tires are thus recycled as energy. The second largest utilization of discarded tires is the further use e.g. for retreading, export, use in agriculture or in port facilities. Thus around 120,000 t are kept in the circulation of materials.
Increasingly, however, discarded tires are also processed in order to be fed into an extensive material recycling process.
As the first steps in the processing of discarded tires for the purpose of producing rubber granulate or rubber meal, the main components are broken down by shredding into the fractions of rubber, steel wire and textile crude lint (tire crude lint or textile fraction). These three fractions may then be roughly separated by sorting. There already exist sufficiently developed processes for processing the rubber granulate into marketable high-grade qualities. The textile and steel fractions, by contrast, are so far not processed in an optimized manner and consequently cannot be recycled in an optimized manner. According to the current state of the processing methods, the steel wire fraction still has rubber adhering to it, which has a negative technical and hence also economic effect on metallurgical recycling. Involving the additional payment of waste disposal fees, the textile fraction is hitherto fed into a thermal removal process or a process of recycling as energy. Currently there exist no methods for processing specifically the textile fraction.
In addition there are certain legal prescriptions, which obligate the manufacturers of vehicle tires or of motor vehicles to ensure the environmentally safe recycling or removal of their products. For handling discarded tires from repair shop waste disposal, there are additionally the obligations that automobile manufacturers in this sector have assumed in connection with the legislation regarding the regulation on packaging. The handling of discarded tires from the recycling of discarded vehicles is furthermore covered by the regulation on discarded vehicles, which stipulates that the manufacturers of vehicles must take back discarded vehicles and their parts and feed them into a recycling process. Beginning in 2015, at least 95 percent by weight of a discarded vehicle must be fed into a reuse and recycling process and of this in turn around 85 percent by weight must be fed into a reuse and material recycling process. In discarded tires, the portion of rubber (rubber, fillers, other) may be assessed at approximately 60%, and the portion of reinforcement materials at approximately 40% (17% steel wire, 23% textile).
German Published Patent Application No. 103 57 968 describes a recycling installation and a method for processing (cold shredding) rubber products and steel-rubber composites such as discarded tires of motor vehicles for example. The processing material is first pre-shredded, is embrittled in a downstream cooling zone, is shredded further in an intermediate shredder, and the shredded and portioned processing material is then ground up and torn up using a post-shredder. The steel and the rubber are exposed and selected using a vibrating table having a connected magnetic separator. The textile reinforcement layers exposed following the shredding processes are to be taken out of the shredded processing material using a separating device in the form of an air sifting device, the separating device preferably being arranged in the form of a blower. The separated textile reinforcement layers are subsequently fed into a packaging process in a textile conveyor device.
German Published Patent Application No. 30 39 870 describes a method for separating rubber and metal in discarded tires, which is supposed to separate, in an economically feasible manner, the metal and the rubber so completely that they are reusable. For this purpose, the discarded tire is first shredded and the metal in the shredded tire is heated in an electromagnetic high-frequency field, whereby the boundary layer of the rubber resting against the metal is thermally disintegrated and the metal can then be separated from the rubber.